Characterizing tectonic and anthropogenic deformation in the Imperial Valley, California, with multitemporal InSAR analysis

Junle Jiang, & Rowena B. Lohman

Under Review April 10, 2020, SCEC Contribution #10073

Despite ongoing improvements and expansion of data catalogs, the effective use of Interferometric Synthetic Aperture Radar (InSAR) remains challenging in actively deforming regions with heavy agricultural activities, where land surface and vegetation changes and soil moisture variability can degrade data quality or introduce confounding signals. Here we use Sentinel-1 satellite imagery to constrain the ground deformation history of 2015--2019 in the Imperial Valley, California, at almost the highest spatial resolutions, to identify and characterize time-variable signals associated with surface soil conditions, shoreline changes, agricultural activities, geothermal power plants, and tectonic motion. In our workflow, the spatial and temporal stability of the interferometric phase are used to assess pixel behavior of disntinct landcover types and identify pixels least likely affected by agriculture. A series of masking, interpolation, and filtering steps are applied to facilitate phase unwrapping, and the unwrapped, unfiltered product is then recovered to reduce artifacts from spatial filtering. Model-based tropospheric corrections and automatic selection of distributed reference points are utilized to improve the spatial and temporal accuracy of InSAR time series, in particular over larger spatial apertures that include topographic variations. The InSAR observations are validated with continuous GPS where available, yielding an agreement of the average velocity within several mm/yr in areas with good data coverage. Discrepancies between InSAR and GPS estimates often exist in areas with lower data quality, and in some cases reveal pronounced signals attributable to surficial processes occuring in the uppermost soil layers. We observe a diverse suite of ground displacement signals over a range of spatial scales, including steady interseismic deformation, seasonal lake-level-modulated subsidence at the East Salton Sea shore, and progressing slow slip on the Superstition Hills fault. In addition, varied deformation signals are observed at four primary geothermal fields within the Imperial Valley. Extensive subsidence at the Salton Sea geothermal field suggests spatial overlap of anthropogenic and tectonic processes, interspersed with potential surficial signals. Geothermal facilities at East Mesa, Brawley, and Heber exhibit smaller or negligible ground deformation, often with temporal variations. Observations of high-resolution, time-variable ground deformation, with characterization of errors when possible, would support efforts to understand subsurface faulting and fluids, manage geothermal operations, and generate robust hazard assessments.

Citation
Jiang, J., & Lohman, R. B. (2020). Characterizing tectonic and anthropogenic deformation in the Imperial Valley, California, with multitemporal InSAR analysis. Remote Sensing of Environment, (under review).


Related Projects & Working Groups
SDOM, Tectonic Geodesy, Geology